Every 2 weeks would work but the wannabe elitists are gonna hate this too because anything other than being able to change for every single boss/dungeon/content is not enough for them.
There was another thing I suggested, let them change covenants like a talent row, but make that account unable to get or use any of the cosmetic rewards, mounts or title.
They want performance above all, they should get it, but they should be ok with forfeiting everything else.